1. Technical Field
This application relates to mobile telecommunications systems in general, having particular application in UMTS (Universal Mobile Telecommunications System) in general, and in particular relates to an apparatus and method of ciphering in wireless telecommunications user equipment operative with a plurality of radio access networks.
2. Description of the Related Art
In a typical cellular radio system, a wireless telecommunication device communicates via one or more radio access radio networks (RANs) to one or more core networks. In UMTS system such devices are typically referred to as User Equipment (UE) and in GSM such devices are typically referred to as Mobile Stations (MS). Such devices comprise various types of equipment such as mobile telephones (also known as cellular or cell phones), lap tops with wireless communication capability, personal digital assistants (PDAs) etc. These may be portable, hand held, pocket sized, installed in a vehicle etc and communicate voice and/or data signals with the radio access network.
In the following, reference will be made to UMTS, GSM and to particular standards. However it should be understood that the invention is not intended to be limited to any particular mobile telecommunications system.
A radio access network covers a geographical area typically divided into a plurality of cell areas. Each cell area is served by at least one base station, which in UMTS may be referred to as a Node B. Each cell is typically identified by a unique identifier which is broadcast in the cell. The base stations communicate at radio frequencies over an air interface with the UEs within range of the base station. Several base stations may be connected to a radio network controller (RNC) which controls various activities of the base stations. The radio network controllers are typically connected to a core network.
GSM is a so-called second generation public land mobile telecommunications system. UMTS is a third generation public land mobile telecommunication system. Various standardization bodies are known to publish and set standards for UMTS, each in their respective areas of competence. For instance, the 3GPP (Third Generation Partnership Project) has been known to publish and set standards for GSM (Global System for Mobile Communications) based UMTS, and the 3GPP2 (Third Generation Partnership Project 2) has been known to publish and set standards for CDMA (Code Division Multiple Access) based UMTS. Within the scope of a particular standardization body, specific partners publish and set standards in their respective areas.
In telecommunications, typically ciphering is used to reduce the likelihood of unauthorised interception and examination of the content of data transmitted between the mobile device and the network. Signalling protocols are typically used to set up ciphering within radio connections and ciphering information is transmitted between the wireless communications device and the network. Issues may arise when a wireless telecommunications device handovers during a call from operating with a first radio access network to a second radio access network. For instance, the ciphering protocol used in the first radio access network may not be appropriate for the second radio access network.
There are thus proposed strategies for apparatus and a method of ciphering in wireless telecommunications devices operative with a plurality of radio access networks. A number of such strategies are detailed below.
Other aspects and features of the proposed strategy will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of apparatus and methods of ciphering in wireless telecommunications user equipment operative with a plurality of radio access networks.
The same reference numerals are used in different figures to denote similar elements.